1. Field of the Invention
The present invention relates to systems for adjusting the white balance of a plurality of color television cameras, and more specifically, to a white balance adjusting system which can eliminate the need to compensate for an error caused by a difference between the reference values of the cameras and an error caused by a video switching system.
2. Description of the Prior Art
Recently, an automatic adjustment system for use in broadcasting color television cameras (hereinafter, referred to as color cameras) has been put to practical use, so that troublesome registration and white balance adjustments, which have so far been conducted by experienced operators, can be achieved in a short time with use of a microcomputer and the like.
In such a system, adjustment of a camera is automatically effected wherein a value corresponding to an adjustment item is detected from a video signal generated from the each color camera and the detected value is compared with a reference value, so as to lie within an allowable range. However, this type system has a problem in that automatic white balance adjustment is unsatisfactory although registration adjustment can be achieved with a high accuracy. In a television program production, three to six color cameras are generally used and the color tone among these cameras must coincide with one another, which depends largely on the accuracy of the white balance of these cameras.
When the above automatic adjustment color cameras are used in the program production, in order to obtain a white balance coincidence among the cameras, the white balance reference values of each camera must be adjusted to be equal, or a single reference value must be applied to the respective cameras. In the latter case, applying the single reference value to the respective cameras through an distributing system will cause an error, requiring re-adjustment.
After the white balance adjustment has been completed, the video signals from the cameras are sent to a video switching unit where the respective video signals are selected through its switching operation. In switching of the video switching unit, by the unbalance of cable loss and differences of terminal matching characteristics among the video signals, gains of the video signals may become different from each other, causing the lost of the white balance. Thus, further re-adjustment must be made manually.